The new terrorist threat to destroy aircraft with bombs exploits an unprotected channel of entry onto the plane, checked baggage, and threatens the plane and all the people aboard.
Various techniques have been suggested to attempt to close off this entry portal. Passenger baggage reconciliation, psychological profiling, interviewing, trained dogs, and, recently, thermal neutron analysis have all been tried on a limited basis. But the wreckage of Pan Am Flight 103 provides dramatic evidence that these efforts have been insufficient. New techniques must be developed and implemented.
In a continuing in-house funded research program, American Science and Engineering, Inc. (AS&E) has developed a completely new technique for X-ray imaging called backscatter imaging. The scatter image differs from the standard image in two important ways. First, the contrast for explosives in an image is dramatically increased and, second, the image confusion is dramatically decreased.
AS&E is developing a system called AS&E EDS (Explosive Detection System), which is based on measuring the bulk X-ray characteristics of scatter images of checked baggage. In the simplified version of this system, the basic hypothesis is that normal checked baggage as a group has rather similar scatter characteristics. We obtained bags from a lost baggage agency to test this hypothesis.
Of 29 bags 58 images were taken, and a particular measure of the scattering characteristics was made. These data were used to develop standard characteristics. Several simulated bombs were added to some of the bags, and the changes in the characteristics were used to develop an automatic detection algorithm.
Although the research is preliminary, the system was able to achieve automatic detection of 2.3-1b (1.04-kg) bombs 100% of the time (five of five) with only a 2% false alarm rate. It was able to detect 80% (four of five) of the 0.7-1b (0.32 kg) bombs with a similar false alarm rate. These and additional data are described in detail.